Field of Invention
The present invention relates generally to the field of plain bearings and materials for use therein. More specifically, the present invention relates to a low friction resin-based surface applied to a metal backing to form a high performance, self lubricated plain bearing.
Description of the Related Art
Conventional metal polymer plain bearings with polymer based sliding surfaces are typically composed of two-layer or three-layer composite bearing structures. Both forms rely on a metal backing to provide rigidity and allow the material to be formed into the appropriate shape, more commonly a cylinder. The metal polymer two-layer bearing materials typically rely on directly-applied or adhered polymers. The design of the three-layered bearing typically rely on an adhesive or porous metallic interlayer to attach the polymer bearing lining to the metal backing. In the latter, the porous metallic interlayer is often a critical part of providing the appropriate load bearing and tribological characteristics as well as functioning as a mechanical key.
Each of these bearings can be useful in dry applications where the use of externally supplied lubricants may be difficult or undesirable.
FIG. 1A shows a cross-section of a conventionally formed three-layer bearing. A porous metallic layer 100 is filled with polymer bearing material 110 and applied to a backing material 120, such as steel. The polymer bearing material 110 has a base polymer, such as polytetrafluoroethylene (PTFE) and filler particles. The porous metallic layer 100 typically has bronze or copper particles sintered to the backing material.
FIG. 1B shows a conventional process for impregnating a polymer bearing material into a porous metallic layer on a metal backing which typically includes spreading a paste or dry powder onto the porous metallic layer, and the paste or dry powder is compacted into the pores via rolling. The paste or dry powder may be made by mixing an aqueous dispersion of PTFE with a filler material, together with an organic lubricant, and coagulating the dispersion to form a “mush.” Once the polymer bearing material is compacted into the porous layer, the backing material can be heated using a furnace to drive off any residual water and lubricant in the polymer bearing material.
The conventional porous metal layer of the three-layer bearing material is typically necessary for attaching the polymer bearing material to the metal backing in such a way as to make the bearing useful in highly loaded, demanding and substantially dry, non-lubricated environments. Without the porous metallic layer, the polymer material will not directly fuse with the metal backing as to provide sufficient strength, adherence or provide the necessary tribological properties, such as wear resistance, fatigue resistance, erosion resistance, low friction and self lubricity for use in highly loaded dry environments. There is a need to reduce the reliance on bronze in this bearing type in order to increase its corrosion resistance and ensure a more constant wear rate and level of friction over the operating life. As a result, there is a need for a metal-free method of fastening or applying the polymer bearing material to the metal backing without compromising the exceptional tribological properties (e.g. wear resistance) normally attained from the bronze/polymer surface combination.